<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <script>
    var year = prompt('请输入年份');
    if (year % 4 === 0 && year % 100 !== 0 || year % 400 === 0) {
      alert(year + '是闰年');
    } else {
      alert(year + '不是闰年');
    }
  </script>
</body>
</html>